Receiving circuit



Nov. 3, 1936. H. E. HOLLMANN RECEIVING CIRCUIT Filed April e, 1934 2Sheets-Sheet 1 M M D TM my m a 5 5 b E MT: t k ATTO R N EY Nov. 3, 1936.H. E, HOLLMANN 2,059,581

' RECEIVING CIRCUIT Filed April 6, 1934 2 SheetsSheet 2 l T E 5 I 7INVENTOR l L Han/s fQ/CH/YOLLMANA/ ATTORNEY Patented Nov. 3, 1936 UNITEDSTATES PATENT OFFICE RECEIVING CIRCUIT tion of Germany Application April6, 1934, Serial No. 719,285

.In Germany April 6, 1933 a 9 Claims.

The present invention relates in general to receiving circuits, and inparticular to receiving circuits comprising tubes operated according tothe so-called retarding field method.

As it is well known in the art, the so-called retarding field circuit,as investigated by Barkhausen and Kurz, Gill and Morrell and others, ischaracterized by the application of a high positive potential Eg to theintermediate or grid electrode of a discharge tube comprising at leastthree electrodes, while a polarizing potential Eb, preferably of a smallnegative value, is applied to the outer electrode, which hereinafter isreferred to as retarding electrode. If the potential Eb is sufficientlynegative, all the electrons, after having passed through the intersticesof the grid electrode, are slowed down and caused to travel in reversedirection towards the intermediate electrode. If the potential of theretarding electrode becomes more positive, a current ib, which may betermed the retarding current, begins to fiow to the retarding electrode.The diagram representing the function ib=f (Eb) hereinafter will bereferred to as the retarding current characteristic. If the potential Egof the intermediate electrode is sufficiently high, the cathode emits aconstant or saturation current which is independent of any variation ofthe voltages applied to the cold electrodes, provided that the gridpotential never grows less than the saturation voltage. In this case thesum of the currents flowing to the intermediate or grid elec-.

trode (ig) and to the retarding electrode (ib) is equal to theconstantsaturation current. This relation may be expressed by thedifferential equation: dig-dih- This expresses in an obvious form, thatthe retarding current is subtracted from the grid current. Therefore theretarding current characteristic is a reflected image of the gridcurrent characteristic, which represents the relation between theretarding potential Eb and the grid current i It is obvious from thisthat the existence of a retarding current is the supposition for thepossibility to control the discharge in a retarding field tube.Experimental investigations have proved that the rectifying effect ofthe retarding field tube depends upon the curvature of the dischargecharacteristic. Therefore the rectifying action of a retarding fieldtube or retarding audion is not limited to extremely high frequenciesbut is also applicable to lower frequencies. Usually the control voltageto be demodulated is applied to the retarding electrode and the powercQnsumed in the input circuit is taken from the control voltage source.

The principal aim of the present invention is to dispense with thecontrol power consumption.

Another object is to provide a satisfactory receiving circuit for allwavelengths used in radio communication service.

Other objectswill become apparent in the following detailed descriptionin connection with the accompanying drawings, wherein:

Fig. 1 represents the characteristic curves of a retarding field tube;

Figs. 2 and 3 are schematic wiring diagrams of receiving circuitsaccording to the invention;

Fig. 4 shows a special construction of an electrode system;

Fig. 5 is a wiring diagram of a modified receiver; and

Fig. 6 is a circuit diagram of an ultra short wave receiving set.

The present invention is based on the fact that, due to the relationbetween the currents flowing to the intermediate or grid electrode andto the retarding electrode mentioned above, the current variationscaused in the circuits connected. to these electrodes by the rectifyingaction of the tube are equal in amount but of opposite direction.Referenceis taken now to the Fig. 1, wherein the retarding current isand the grid current i are plotted against the retarding electrodevoltage eb. According to the present invention the control voltage isapplied not only to the retarding electrode but also to the intermediateor grid electrode. In this way the current variations compensate eachother with regard to the control voltage, i. e. the internal inputimpedance of the tube is infinite and no control power is consumed atall.

For a better understanding of the invention and for an illustration of apractical form of circuits in which it may be embodied, reference may behad to Fig. 2, wherein the wiring diagram of a receiver is represented.The receiver comprises a tube V containing a filamentary cathode K, agrid electrode G and a retarding electrode B. A high positive voltage isapplied to the grid G by the battery Eg, while the retarding electrode Bis negatively biased by the battery Eb. The radio frequency signalscollected by the antenna system A are induced in the input circuit E andsimultaneously supplied to the retarding electrode B and, bymeans of thecondenser C, to the grid electrode G, so that the power consumed in theretarding electrode circuit is restored from the positively charged gridelectrode. The condenser C serves only to separate the differentunidirectional voltages applied to the grid and the retarding electrodeand should offer a low impedance path to the radio frequency waves. Inorder to prevent the radio frequency current from leaking away into thegrid circuit, a high frequency choke coil D may be inserted in the gridcircuit.

By properly adjusting the biasing potential of the retarding electrodeEb the operating point is located near the upper or the lower bend ofthe characteristic curve, e. g. on point a; or b in Fig. 1. Then arectification of the radio frequency signals takes place, whereby themodulation frequency impressed on the carrier wave may be taken off bymeans of a low frequency transformer T inserted in the grid circuit.

A modified wiring diagram of a receiving circuit is illustrated in Fig.3. The radio frequency signals collected by the antenna A and induced inthe input circuit E are supplied directly to the grid electrode andthrough a condenser C to the retarding electrode. The primary coil ofthe transformer T is bridged by a by-pass condenser C providing a lowimpedance alternating current path for the incoming radio frequency. Theretarding electrode biasing potential is supplied through a choke coil Dpreventing the high frequency from leaking away into the battery Eb.

A full compensation for the control current is accomplished only if thecondenser C acts as short-circuit for the control frequency. If thecapacity C, however, gradually is diminished beginning from very largevalues, a phase displacement takes place between the alternatingvoltages supplied to the retarding electrode and to the grid, whichcauses self-excitation of the circuit. Therefore, when the condenser Cis made variable, the excitation may be adjusted in an exceedinglysimple and comfortable manner and the sensitivity of the retardingaudion thereby considerably increased.

In the Figs. 2 and 3 the condenser C is depicted as a separate circuitelement. If the variation of the regenerative effect is dispensable, thecondenser C may be located within the evacuated container or evenconstructively combined with the electrodes. This arrangement may be ofparticular advantage when extremely high frequencies are used. Apractical form of an electrode system according to this invention isschematically illustrated in Fig. 4. The retarding electrode B forms theone condenser armature, while the other consists in a metal tube R,which is slipped over the retarding electrode B and is insulatedtherefrom by the dielectric D. The metal tube R is immediately connectedto the grid electrode G.

In practice the exact adjustment of the retarding potential by means ofthe battery Eb means an additional voltage source, which may be avoidedby connecting the retarding electrode through a high ohmic resistance toa positive potential. This is illustrated in Fig. 5, which is amodification of the circuit diagram shown in Fig. 3. The retardingelectrode B is connected through the high frequency choke D and the highresistance W to the positive terminal of the grid battery Eg. When theresistance W is variable, the operating point may be easily adjusted tothe optimal position. In order to draw a rectified current as large aspossible, the resistance W is short-circuited for the modulationfrequency. For this reason the resistance W is bridged by a very largecapacity C".

The method of controlling a retarding field tube without any powerconsumption is of particular advantage in the ultra short wave range.Fig. 6 illustrates a receiving circuit diagram especially adapted forextremely short wave work. The resonance system comprises a lecherparallel wire system L, L, which is tuned by slidable reflecting bridgesR and R. and which is excited by a dipole antenna Di. In the voltageloop the tube V is located, the grid and the retarding electrode ofwhich are capacitively connected within the bulb. Both electrodes arecontinued by the lecher wires L, which supply biasing potentials tothese electrodes. The filament is interconnected between the lecherwires L serving as heating current leads. The retarding electrodebiasing potential is developed across the high resistance W, which isparalleled by the condenser C" of very large capacity. The modulationfrequency may be taken off from the grid circuit by means of the lowfrequency transformer T, the primary coil of which is bridged by theby-pass condenser C forming a radio frequency short circuit. Whendecimeter waves are received, regeneration may be obtained by adjustingthe grid potential Eg.

What is claimed is:

1. Radio receiving apparatus for ultra short wave Work comprising aretarding field tube having a cathode, a grid electrode and a retardingelectrode, a condenser interconnected between the grid and the retardingelectrode, and a parallel wire system, the cathode being inserted intoone parallel wire and the retarding electrode and the grid beinginserted into the other parallel Wire.

2. In combination, an electron discharge device having within anenvelope an anode, cathode and control electrode, means for applying ahigh positive potential to said control electrode and a much lowerpotential to said anode relative to said cathode, a metallic elementwithin said envelope in juxtaposition to said anode and formingtherewith a condenser, a direct connection between said controlelectrode and said metallic element, and a high frequency tunable inputcircuit between said'cathode and one of said other electrodes.

3. In a high frequency circuit, an electron discharge device comprisingwithin an envelope, a cylindrical anode, a straight linear cathodewithin said anode and concentrically positioned with respect thereto,and a control electrode located between said cathode and said anode andextending the length of said anode, means for supplying a high positivepotential to said control electrode and a much less potential to saidanode relative to said cathode, a cylindrical metallic element injuxtaposition to said anode and forming therewith a condenser, oneterminal of said control electrode being connected to one end of saidelement and the other terminal of said control electrode being connectedto the other end of said element.

4. An ultra short wave receiver comprising an electron discharge devicehaving within an envelope, a cathode, an anode and a control electrodebetween said anode and cathode, means within said envelope forcapacitively coupling said control electrode and anode together, alecher wire system comprising two parallel wires and a movable condenserbridge across said wires, said cathode being connected to one of saidparallel wires and said control electrode to the other of said parallelwires.

5. An ultra short wave receiving system having in combination, anelectron discharge device comprising within an envelope, a cylindricalanode, a straight linear cathode within said anode and concentricallypositioned with respect thereto, and a control electrode located betweensaid cathode and said anode and extending the length of said anode, acylindrical metallic element in juxtaposition to said anode and formingtherewith a condenser, one terminal of said control electrode beingconnected to one end of said element and the other terminal of saidcontrol electrode being connected to the other end of said element, atwo parallel wire system having movable condenser bridges substantiallyat both ends thereof, said cathode being serially connected in one ofsaid parallel wires, and the capacitive coupling between said controlelectrode and anode being serially connected in the other of saidparallel wires, and means for supplying a high positive potential tosaid control electrode and a much smaller potential to said anoderelative to said cathode.

6. An ultra short wave receiving system having in combination, anelectron discharge device comprising Within an envelope, a cylindricalanode, a straight linear cathode within said anode and concentricallypositioned with respect thereto, and a control electrode located betweensaid cathode and said anode and extending the length of said anode, acylindrical metallic ele ment in juxtaposition to said anode and formingtherewith a condenser, one terminal of said control electrode beingconnected to one end of said element and the other terminal of saidcontrol electrode being connected to the other end of said element, atwo parallel wire system having movable condenser bridges substantiallyat both ends thereof, said cathode being serially connected in one ofsaid parallel wires, and the capacitive coupling between said controlelectrode and anode being serially connected in the other of saidparallel wires, and means for supplying a high positive potential tosaid control electrode and a much smaller potential to said anoderelative to said cathode, an audio frequency transformer having primaryand secondary windings, a utilization circuit, said primary windingbeing in circuit with one of said parallel wires and said secondarywinding being coupled to said utilization circuit.

'7. An ultra short wave receiver having, in combination, an electrondischarge device having within an envelope an anode, cathode and controlelectrode, means for applying a positive potential to said controlelectrode and a much lower potential to said anode relative to saidcathode, means for capacitively connecting said anode and controlelectrode together, a parallel tunable resonant circuit, one terminal ofwhich is connected to said cathode and the other terminal to one of saidother electrodes, an antenna coupled to said parallel resonant circuit,and a utilization circuit coupled to said connection from the resonantcircuit to said cathode.

8. In combination, in a receiver, a braking field type of electrondischarge device having within an envelope an anode, cathode and controlelectrode, means for applying a high positive potential to said controlelectrode and a much lower potential to said anode relative to saidcathode, a capacity connecting said anode and control electrodetogether, a high frequency tunable input circuit, a radio frequencyconnection between said cathode and input circuit, and a connectiondevoid of concentrated reactance between said input circuit and one ofsaid other electrodes, and a high frequency choke coil between saidremaining electrode and said means.

9. An ultra short wave receiver comprising an electron discharge devicehaving within an envelope, a cathode, an anode, and a control electrodebetween said anode and cathode, means within said envelope forcapacitively coupling said control electrode and anode together, alecher wire system comprising two parallel wires and a movable condenserbridge across said wires, said cathode being connected to one of saidparallel wires and said anode to the other of said parallel wires.

HANS ERICH HOLLMANN.

